How is non-invasive Down syndrome screening performed?
Jul 21, 2025
Source: Cainiu Health
Dr. Zhang Lu
Introduction
Under normal circumstances, Down syndrome screening with non-invasive testing, also known as non-invasive prenatal genetic testing, is a method used to assess the risk of fetal chromosomal abnormalities by analyzing cell-free fetal DNA in the mother's blood. The testing process mainly includes making an appointment in advance, preparation for the test, sample collection, laboratory analysis, and obtaining the results. A detailed explanation is as follows:
Generally, non-invasive prenatal testing (NIPT), also known as non-invasive prenatal genetic testing, is a method that evaluates the risk of fetal chromosomal abnormalities by analyzing fetal free DNA in the mother's blood. The testing process mainly includes prior appointment scheduling, preparation for the test, sample collection, laboratory testing, and obtaining the results. The details are as follows:
1. Prior Appointment Scheduling
Pregnant women should choose a regular hospital's obstetrics and gynecology department or prenatal diagnostic center, and schedule an appointment for NIPT via the hospital's official website, by phone, or by on-site registration. During the appointment, they should inform the medical staff of the date of their last menstrual period and their prenatal examination status. The doctor will confirm whether the gestational age meets the testing requirements and explain the precautions and required documentation for the test.
2. Preparation for the Test
On the day of testing, fasting is not required, and normal eating and drinking are allowed. Upon arrival at the hospital, check in at the registration desk first, then proceed to the designated clinic where the doctor will verify information including gestational age, medical history, etc. Once contraindications for testing are ruled out, the pregnant woman will sign an informed consent form, clearly stating the purpose, risks, and limitations of the test.
3. Sample Collection
In the sampling room, medical staff will collect 5-10 milliliters of peripheral blood via venipuncture from the elbow using a disposable needle. The blood collection process is similar to routine phlebotomy and takes about 1-2 minutes. After the blood draw, apply sterile cotton swabs to the puncture site for 5-10 minutes until the bleeding stops, and then normal activities can resume without special care. The collected blood samples will be labeled with relevant information and sent to the laboratory.
4. Laboratory Testing
After receiving the sample, the laboratory will extract and purify fetal free DNA from the blood. Using genetic sequencing technology, the extracted DNA is analyzed to determine whether the number of chromosomes 21, 18, and 13 are normal, thereby assessing the risk of the fetus having related trisomy syndromes. The entire testing process takes approximately 7-10 working days, during which the laboratory will strictly control the quality to ensure the accuracy of the results.
5. Obtaining Results
Once testing is completed, the hospital will notify the pregnant woman to obtain the report via text message, phone call, or in person. The report will clearly indicate the risk level of the fetus having diseases such as trisomy 21 syndrome. After receiving the report, it should be promptly given to a doctor for interpretation. If the result is low-risk, regular prenatal check-ups can continue. If the result is high-risk, the doctor will recommend further diagnostic tests such as amniocentesis.
If the test results are abnormal, pregnant women should communicate promptly with their doctors and follow medical advice for further examination and management. Throughout the entire pregnancy, women should follow their doctors' recommendations and attend all scheduled prenatal examinations to ensure healthy fetal development.
